A photosensitive material forming a photosensitive member, inorganic photoconductive materials such as selenium, cadmium sulfide or zinc oxide have been known.
These photosensitive materials have such many advantages that those materialis can be charged to adequate potential, the loss of charges in the dark is low, the electrical charge can be dissipated fast with irradiation of light and so on. However, they have disadvantages as follows. For example, a photosensitive member based on selenium has difficulty in its production, high production costs and difficult handling due to inadequate resistivity to heat or mechanical impact. A photosensitive member based on cadmium sulfide or zinc oxide has such defects as its unstable sensitivity in a highly humid environment and less stability with time because of the deterioration of dyestuffs added as a sensitizer by corona charge and fading with exposure.
On the other hand, many kinds of organic photoconductive materials such as polyvinylcarbazole and so on have been proposed. These organic photoconductive materials are superior in film forming properties, lightness in weight, etc., but inferior in sensitivity, durability and environmental stability to aforementioned inorganic photoconductive materials.
Various studies and developments have been in progress to overcome the above defects and problems, and a function-divided photosensitive member of a laminated type or a dispersed type has been proposed in which charge generating function and charge transporting function are divided by different layers or different dispersed materials. The function-divided photosensitive member can be a highly efficient photosensitive member in electrophotographic properties such as chargeability, sensitivity, residual potential, durability against copy and repetition because most adequate materials can be selected from among various kinds materials. Further, the function-divided photosensitive member has high productivity and low costs, since it can be prepared by coating, and adequately selected charge generating materials can freely control a region of photosensitive wavelength. Illustrative examples of such charge generating materials are organic pigments or dyes such as phthalocyanine pigment, cyanine pigment, polycyclic quinone pigment, perylene pigment, indigo dye, thioindgo dye, squaraine compounds, etc.
In particular, a phthalocyanine pigment is useful as a charge generating material to a laser printer of electrophotographic type furnished with laser light as light source, which is one kind of high speed printers. Among phthalocyanine pigments which have high sensitivity in the range of long wavelength, metal-free phthalocianine pigments such as .tau.-form, modified-.tau.-form, .eta.-form, and modified-.eta.-form are disclosed in Japanese Patent KOKAI Nos. 18263/1983, 19147/1985 or 19153/1985. Japanese Patent KOKAI No. 19147/1985 discloses a photosensitive member in which a charge generating layer comprises .tau.-form or modified-.tau.-form phthalocyanine at a ratio of 1/3-3/1 to silicon resin. Such photosensitive member, although, have not enough static characteristics, and more sensisitive improvement is desired.
On the other hand, a function divided photosensitive member in which a charge transporting layer is comprised of hydrazone compounds generally used as charge transporting materials brings about such problems as the deteriorations of chargeability and the increment of residual potential when left alone in the light. The properties in the light are liable to be deteriorated when a photosensitive member is exposed to light for its installation in a copying machine or the maintenance of a copying machine. Some photosensitive members are deteriorated by the repeated irradiations of erasing light in a copying machine.
It is conventionally thought that the light deterioration is caused by ultraviolet light in the range of 450 nm or less. From the view point, photosensitive member containing a ultraviolet absorber or a dye which absorbs ultraviolet light of 450 nm or less are disclosed in Japanese Patent KOKAI Nos. 120260/1983, 163945/1983, 163946/1983 and so on.
But, the overcome of light deteriorations requires a large amount of dyes, which prevent the movement of carriers and causes the decrease of charge mobility in a charge transporting layer.